This invention relates to new and improved method of and means for controlling skew, bow and yield in circularly knit pile fabric, and more particularly for controlling those conditions during advance of the split and spread web or strip of the fabric incident to tentering.
The problems of skew, bow and yield have been present in the production and treatment of circularly knit pile fabrics from the beginning of such production, and have become more critical since the introduction of patterned knit pile fabrics.
In the production of deep pile fabric in a circular knitting machine, course after course is knit by means of a rotating needle cylinder, and fibers are incorporated in the stitches as the yarn is knit into the fabric. Prior to the formation of a stitch, each of a number of needle hooks rises into carded fiber on the surface of a respective doffer roll, engaging and drawing down a tuft of fiber which is to be incorporated into the stitch. An air jet blows over each needle as the stitch is being formed to aid in orienting the fibers taken by the needle and causing the ends of the fibers to stream toward the center of the tubular form of the knit fabric whereby the pile is developed at the inner surface of the tubular form and the outer surface of the tubular form is free from pile and serves as the back of the fabric. Beyond the needle cylinder, either in the knitting machine or subsequently, the knitted pile fabric tube is slit longitudinally, so that for further processing the fabric can be handled in a spread apart web or strip. By way of example, apparatus is disclosed in U.S. Pat. No. 3,999,405, in which slitting is efficiently done in the same machine sequentially after the circular pile fabric knitting step, and for convenience, the present disclosure will be related to this type of apparatus.
For further processing, the slit tubularly knit pile fabric is spread out to generally flattened condition and run through a tenter. Because of the nature of the knit fabric, skew, bow and yield present special problems which are aggravated where the pile fabric is patterned. Generally, manual controls have been employed requiring constant observation and manual correction of the moving fabric, but resulting in up to 30% rejection of fabric and thus substantial economic loss. The majority of rejects have been for too much skew, although bow and yield complicate the situation.
Various attempts have been made heretofore in the woven fabric industry to alleviate the problems of skew, bow and yield, but they have not solved the problem for tubularly knit pile fabric, and particularly deep pile patterned knit fabric. One prior example for automatic weft straightening control is found in U.S. Pat. No. 2,638,656, wherein flat woven fabric is provided with relatively wide transverse stripes of fluorescent or phosphorescent pigments extending entirely across the fabric at spaced intervals to be detected by invisible or black light rays for operating weft or bow straightening apparatus upstream from a tenter.
Alleged attainment of substantially uniform yield in woven fabric as it is being variously processed and tentered is disclosed in U.S. Pat. No. 3,839,767, wherein variations in fabric density are detected and corrected by an elaborate mechanical arrangement.
Arrangements such as those in U.S. Pat. Nos. 2,638,656 and 3,839,767 do not satisfactorily meet the special conditions present in respect to circularly knit pile fabric and in particular deep pile patterned knit fabric.